It's not easy to achieve the biblical balance between unity and purity. Often Christians press for either unity (catholicity) or purity (orthodoxy), but few are known for both. Those who want unity tend to sideline or minimize the secondary teachings of the Bible. Those who want purity often elevate secondary teachings to a place of primary importance. But both approaches are idolatrous. I confess that I don't get this right, but I want to.
The Idol of Purity
Christians who emphasize doctrinal purity tend to make secondary biblical teachings central to their personal identity. Instead of being centered on Christ, they're centered on being “Calvinists” or “Arminians,” “Fundamentalists” or “Evangelicals,” “Credobaptists” or “Paedobaptists,” “confessionalists” or “biblicists,” "biblical theologians" or "systematic theologians," “social ministry oriented” or “conversion ministry oriented,” “family integrated” or “age graded,” etc. Those who idolize purity turn secondary convictions into objects of worship. And the result is that their idols enslave them. They hate and fear whatever and whoever opposes their idols. They exclude true Christians from fellowship. They cause divisions within the body of Christ. They give lip service to the centrality of Christ, but their chief concerns lie elsewhere.
Those who idolize purity are proud of their distinctiveness. They feel superior to other Christians because they've got something right that other Christians don't. So they judgmentally condemn those who don't think like they do. They're often unteachable and unwilling to listen and learn from others.
The Idol of Unity
Christians who emphasize unity tend to minimize and sideline secondary doctrines. They speak of unity in Christ, but it's often a very shallow unity. They rightly fellowship with Christians who have a wide range of beliefs, but they won't speak the whole counsel of God in love. Their idol of unity enslaves them. From fear of disunity, they avoid certain truths, which, if spoken, may contribute to the health of fellowship. Ironically, they even refuse fellowship with those who thoroughly teach the secondary truths of Scripture. They give lip service to Christian unity, but in practice, they only unite with those who are “catholic” like they are.
Those who idolize unity proudly mute the Word of God. They refuse to speak clearly where Christ has spoken. They refuse to insist on the whole counsel of God and to show how secondary truths are necessary supports to the gospel itself. They feel superior to other Christians because they are “big enough” to join with Christians across a broad spectrum of belief. They have superior and judgmental attitudes toward those who aren't like them. They're often unteachable and refuse to learn from others.
Truth and Unity in Jesus Christ
Instead of idolizing doctrines/confessions (purity) or people/church (unity), we need to center on Jesus.
Against the “Purity Idol.” If our identity is in Jesus, we don't need to feel personally threatened if someone disagrees with us. We are “right” in Christ, not in our doctrine. That means we don't have to prove ourselves right. We don't have to fix everyone else's beliefs. We can let others correct our thinking with the Word of God. We can love and draw near to our brothers and sisters in Christ, even if they're wrong about important secondary doctrines because that's how Christ treats us. Jesus lovingly drew near to us, while we were still heretics.
Against the “Unity Idol.” If our identity is in Jesus, we don't need to fear speaking the whole counsel of God in love, and we don't need to be offended by those who do. We're objectively united to Christ and with all believers in Christ, which means disagreements cannot separate us, and we don't need to fear that they will. We can humbly and boldly contend earnestly for the truth of secondary doctrines, and so love our brothers, without fearing the loss of true unity. Jesus lovingly told us the whole truth, while lovingly uniting Himself to us. We can be like Him.